Low-light video frame enhancement

ABSTRACT

A method of combining image data from multiple frames to enhance one or more parameters of video image quality includes acquiring a first image at a first exposure duration, as well as acquiring a second image at a second exposure duration shorter than the first exposure duration and at a time just before, just after or overlapping in time with acquiring the first image, such that the first and second images include approximately a same first scene. In this way, the second image is relatively sharp and under-exposed, while the first image is relatively well-exposed and less sharp than the second image. Brightness and/or color information are extracted from the first image and applied to the second image to generate an enhanced version of the second image.

RELATED APPLICATIONS

This application is a Continuation-in Part (CIP) of U.S. patentapplication Ser. No. (U.S. Ser. No.) 12/330,719, filed Dec. 9, 2008,which is a CIP of U.S. Ser. No. 11/856,721, filed Sep. 18, 2007, whichclaims priority to U.S. provisional application No. 60/893,116, filedMar. 5, 2007. This application is also related to U.S. Ser. No.12/336,416, filed Dec. 16, 2008; and U.S. Ser. No. 11/753,098, filed May24, 2007; and U.S. Ser. No. 12/116,140, filed May 6, 2008. All of theserelated applications are assigned to the same assignee and are herebyincorporated by reference.

BACKGROUND

1. Field of the Invention

The present invention relates to an image processing method andapparatus.

2. Description of the Related Art

Sensor arrays for digital cameras exist for capturing color photos.Sensors known as RGBW sensors are used for capturing red, green, andblue colors, and for capturing luminance information for multiple pixelsof an array of pixels. The red, green and blue pixels include filterssuch that only certain narrow ranges of wavelengths of incident lightare counted. The white pixels capture light of red, green and bluewavelengths, i.e., of a broader range of wavelengths than any of theblue, green and red pixels. Thus, the white pixels are typicallybrighter than any of the blue, red and green pixels if they are exposedfor the same duration.

Noise removal algorithms can tend to blur face regions in an undesirablemanner. Noise removal algorithms are described at U.S. patentapplication Nos. 11/856,721 and 11/861,257, which are herebyincorporated by reference, as are U.S. Ser. Nos. 10/985,650, 11/573,713,11/421,027, 11/673,560, 11/319,766, 11/744,020, 11/753,098, 11/752,925,and 12/137,113, which are assigned to the same assignee as the presentapplication and are hereby incorporated by reference.

Kodak has developed a RGBW color filter pattern differing from thepreviously known Bayer Color Filter. The RGBW pattern of Kodak isreferred to as a Color Filter Array (CFA) 2.0. One half of cells in aRGBW pattern are panchromatic, i.e. sensing all of the color spectrum (Ycomponent)—usually called white cells. This way more light energy isaccumulated in the same amount of time than for color pixels. A Bayerfilter uses only ⅓ (˜0.33) of color spectrum energy. An RGBW filter uses4/6 (˜0.67) of the energy, where ½ comes from white cells and ⅙ from RGBcells.

CFA Array looks something like the following:

WBWG . . .

BWGW . . .

WGWR . . .

RWRW . . .

In this context, the following are incorporated by reference: U.S. Pat.Nos. 7,195,848, 7,180,238, 7,160,573, 7,019,331, 6,863,368, 6,607,873,6,602,656, 6,599,668, 6,555,278, 6,387,577, 6,365,304, 6,330,029,6,326,108, 6,297,071, 6,114,075, 5,981,112, 5,889,554, 5,889,277,5,756,240, 5,756,239, 5,747,199, 5,686,383, 5,599,766, 5,510,215,5,374,956, and 5,251,019.

Two source images nominally of the same scene may be used to produce asingle target image of better quality or higher resolution than eitherof the source images.

In super-resolution, multiple differently exposed lower resolutionimages can be combined to produce a single high resolution image of ascene, for example, as disclosed in “High-Resolution ImageReconstruction from Multiple Differently Exposed Images”, Gunturk etal., IEEE Signal Processing Letters, Vol. 13, No. 4, April 2006; or“Optimizing and Learning for Super-resolution”, Lyndsey Pickup et al,BMVC 2006, 4-7 Sept 2006, Edinburgh, UK, which are hereby incorporatedby reference. However, in super-resolution, blurring of the individualsource images either because of camera or subject motion are usually notof concern before the combination of the source images.

U.S. Pat. No. 7,072,525, incorporated by reference, discloses adaptivefiltering of a target version of an image that has been produced byprocessing an original version of the image to mitigate the effects ofprocessing including adaptive gain noise, up-sampling artifacts orcompression artifacts.

US published applications 2006/0098890, 2007/0058073, 2006/0098237,2006/0098891, European patent EP1779322B1,and PCT Application No.PCT/EP2005/011011 (Ref: FN109), which are each hereby incorporated byreference, describe uses of information from one or more presumed-sharp,short exposure time (SET) preview images to calculate a motion functionfor a fully exposed higher resolution main image to assist in thede-blurring of the main image.

Indeed many other documents, including US 2006/0187308, Suk Hwan Lim etal.; and “Image Deblurring with Blurred/Noisy Image Pairs”, Lu Yuan etal, SIGGRAPH07, Aug. 5-9, 2007, San Diego, Calif., which areincorporated by reference, are directed towards attempting to calculatea blur function in the main image using a second reference image beforede-blurring the main image.

Other approaches, such as may be disclosed in US2006/0017837, which isincorporated by reference, involve selecting information from two ormore images, having varying exposure times, to reconstruct a targetimage where image information is selected from zones with high imagedetails in SET images and from zones with low image details in longerexposure time images.

Nowadays, even though image processing techniques have evolved, stilllow-light scenes tend to lead to very dark frames in videos. By thesemeans the visual quality is low. A solution to this problem is providedherein.

SUMMARY OF THE INVENTION

A method of combining image data from multiple frames to enhance one ormore parameters of video image quality is provided, which uses aprocessor and at least one video acquisition system including a lens andan image sensor. The method includes acquiring a first image at a firstexposure duration, as well as acquiring a second image at a secondexposure duration shorter than the first exposure duration and at a timejust before, just after or overlapping in time with acquiring the firstimage, such that the first and second images include approximately asame first scene. In this way, the second image is relatively sharp andunder-exposed, while the first image is relatively well-exposed and lesssharp than the second image. Brightness and/or color information areextracted from the first image and applied to the second image. Thebrightness and/or color information is/are extracted from the firstimage to generate an enhanced version of the second image enhanced interms of brightness and/or color quality. The enhanced version of thesecond image is displayed, stored, transmitted, and/or streamed within avideo sequence.

The method may further include applying to one or more further imagesthe brightness and/or color information extracted from the first imageto generate enhanced versions of the one or more further images enhancedin terms of brightness and/or color quality. The one or more furtherimages may be acquired at or near the second exposure duration and at atime or times just before or just after, or both, the acquiring of thesecond image, such that the one or more further images includeapproximately the same scene as the first and second images.

The method may also include acquiring a third image at or near the firstexposure duration when a predetermined number of multiple frames hasbeen recorded since the acquiring of the first image. A fourth image mayalso be acquired at or near the second exposure duration and at a timejust before, just after or overlapping in time with the third image,such that the third and fourth images include approximately a samesecond scene different from or same as the first scene. Brightnessand/or color information are extracted from the third image, and appliedto the fourth image to generate an enhanced version of the fourth imageenhanced in terms of brightness and/or color quality. The enhancedversion of the fourth image is displayed, stored, transmitted, and/orstreamed within a video sequence.

The method may further include acquiring a third image at or near thefirst exposure duration when a predetermined amount of camera movementhas been detected since the acquiring of the first image. A fourth imagemay be acquired at or near the second exposure duration and at a timejust before, just after or overlapping in time with the third image,such that the third and fourth images include approximately a samesecond scene different from the first scene due at least to the cameramovement. Brightness and/or color are extracted from the third image,and applied to the fourth image to generate an enhanced version of thefourth image enhanced in terms of brightness and/or color quality. Theenhanced version of the fourth image is displayed, stored, transmitted,and/or streamed within a video sequence.

The method may also include acquiring a third image at or near the firstexposure duration including combining some of the data from the firstimage with some or all of the data from the second image. A fourth imagemay be acquired at or near the second exposure duration and at a timejust before, just after or overlapping in time with the third image,such that the third and fourth images include approximately the samefirst scene. Brightness and/or color information are extracted from thethird image and applied to the fourth image to generate an enhancedversion of the fourth image enhanced in terms of brightness and/or colorquality. The enhanced version of the fourth image is displayed, stored,transmitted, and/or streamed within a video sequence. The method mayinclude repeatedly iterating the method as the scene evolves with timeand/or camera movement.

The method may include iteratively alternating acquisition ofwell-exposed and sharp, under-exposed images; extracting brightnessand/or color information from the well-exposed images; and applying tothe sharp, under-exposed images the brightness or color information, orboth, extracted from the well-exposed images to generate enhancedversions of the sharp, under-exposed images enhanced in terms ofbrightness or color quality, or both; and displaying, storing,transmitting, or streaming the enhanced versions of the sharp,under-exposed images within said video sequence.

The method may also include iteratively performing the following:

acquiring two sharp, under-exposed frames and a well-exposed frame;

extracting brightness and/or color information from the well-exposedframe;

applying to each pair of sharp, under exposed images respectivelycaptured immediately before and immediately after the acquiring of eachwell-exposed frame the brightness and/or color information extractedfrom the well-exposed frame to generate enhanced versions of each of thepair of sharp, under-exposed images enhanced in terms of brightnessand/or color quality; and

displaying, storing, transmitting, or streaming within said videosequence the enhanced versions of the pair of sharp, under-exposedimages.

The method may utilize separate image acquisition subsystems (IAS's) foracquiring the first and second images. The separate IAS's may includefirst and second IAS's, wherein the first IAS is configured to acquireimages at a faster frame rate than the second IAS. The first IAS may bespecially configured to capture relatively sharp, under-exposed imagesand the second IAS may be specially configured to capture well-exposedand less sharp images. The first IAS may have a fixed frame rate. Thesecond IAS may have a variable frame rate configured for capturingoptimally-exposed images under different lighting conditions. The methodmay include acquiring both the first and second images with a same lensas optical input, and splitting the optical input between first andsecond image sensors. The method may alternatively include acquiring thefirst and second images, respectively, with a first lens/sensorcombination and a second lens/sensor combination. In this alternative,parallax correction may be applied.

A digital video acquisition system is also provided, including a lens,an image sensor for capturing a stream of multiple video images, aprocessor and a memory having processor-readable code embedded thereinfor programming the processor to perform any of the methods describedabove or below herein.

One or more processor-readable media is/are also provided which haveprocessor-readable code embedded therein for programming one or moreprocessors to perform any of the methods described above or belowherein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates conventional video frame acquisition.

FIG. 2 schematically illustrates video frame enhancement using luminanceand/or color data from a well-exposed image, and applying the data to arelatively less exposed, sharper image in accordance with a firstembodiment.

Frame 3 schematically illustrates video frame enhancement usingluminance and/or color data from a well-exposed image, and applying diedata to a relatively less exposed, sharper image in accordance with asecond embodiment.

FIG. 4 schematically illustrates video frame enhancement using luminanceand/or color data from a well-exposed image, and applying the data to arelatively less exposed, sharper image in accordance with a thirdembodiment.

FIGS. 5 a-5 d schematically illustrate video frame enhancement usingluminance and/or color data from a well-exposed image, and applying thedata to a relatively less exposed, sharper image in accordance with afourth embodiment which involves at least two image acquisitionsub-systems, so that the well exposed image is captured with a firstsub-system while the sharper image is captured with a second sub-system.

DETAILED DESCRIPTIONS OF THE EMBODIMENTS

Several embodiments are described below that use a pair of images toenhance one of them. Alternative embodiments may be obtained bycombining features of two or more of these embodiments, or by combiningfeatures of one or more of the embodiments with features described inthe background or in any of the references cited there or hereinbelow.In certain embodiments, one of the pair of images is the target image(which is sharp but under exposed and noisy), and another image is thereference image (which is well-exposed but blurred, e.g., motionblurred). In specific embodiments, the use of the method if dedicated toimproving the quality of video-frames acquired in scenes with low light.

For ensuring animation (motion, fluency), the frame-rate in a video isgenerally over a predetermined threshold (e.g., 12 frames/sec). Thisimposes a maximum exposure time for each frame. In low light conditions,this exposure time is not-sufficient for offering good visual quality.Several embodiments are provided herein as solutions to overcome thisproblem. Several methods of improving video capture in low-light areprovided by applying techniques to a continuous sequence of images.Three embodiments generally incorporate modified image processing withina conventional video camera or any later generation camera, while afourth embodiment involves a video camera that incorporates two distinctimage acquisition subsystems.

Image+Video

FIG. 1 schematically illustrates a conventional frame acquisitionprocess. According to the illustration of FIG. 1, multiple video frames110 are sequentially acquired each with a same exposure duration.

FIG. 2 schematically illustrates use of frames with different exposuredurations. A well-exposed frame 210 is acquired at a beginning of avideo acquisition. From this well-exposed image 210, one may extractbrightness and/or color information that are used to enhance the nextframe 220. The next frame 220 is exposed using an exposure determinedfrom a maximum frame-rate. The frame 220 is enhanced with brightnessand/or color information extracted from the well exposed frame 210.

The frame 220 may be displayed (included in the video) and may be usedfor determining or generating another reference image 230 that mayitself be used to enhance the next acquired frame 240 (frame 2). Thereference frame 230 may be generated as a combination of the firstacquired frame 210 and the second acquired frame 220.

The next acquired frame 240 is enhanced with brightness and/or colorinformation extracted from the generated well exposed frame 230. Theframe 240 may be displayed (included in the video) and may be used fordetermining or generating another reference image 250 that may itself beused to enhance the next acquired frame 260. The reference frame 250 maybe generated as a combination of the generated frame 230 and the thirdacquired frame 240. The frame 260 may be displayed (included in thevideo) and the process may be repeated over a complete vide sequence.

The acquisition of the well exposed image may be repeated at certaintimes. A digital camera may be used that has an auto-exposure algorithmthat runs in the video mode. The best exposure time for a frame may beestimated in-camera. The camera may be configured such that a wellexposed image may be acquired only when the auto-exposure demands aperiod larger than the one imposed by the maximum frame rate.

If the entire video is acquired in low light then the amount of timewhen it is needed to repeat the image acquisition may depend on cameramovement. This may be estimated by registration techniques. An examplemethod may be performed by a processor as follows:

-   -   1. Test for Low-Light Case: the auto-exposure determined time is        approximately equal to the maximum frame rate. The test should        run continuously no matter which is the current case.    -   2. When the conditions are such that it is not a Low-Light Case,        then normal acquisition may be performed with record of any well        exposed image.    -   3. When the conditions are such that it is a Low-Light Case,        then:        -   a. Acquire a well exposed image and iteratively run the            enhancing method for each video frame;        -   b. Estimate the camera movement by performing registration            on the recorded frames. If the motion is larger than a            threshold (the image content has significantly changed,            e.g., 30% from the last well exposed image), then acquire a            new well-exposed image; and        -   c. If a certain number of video frames (e.g., M=5, 10, 20,            30, 40, 50, 60, 75, or 100 or more) has been recorded from            the last well-exposed image, then acquire a new well exposed            image.

Video Frame Pairs with Modified Exposure Time

FIG. 3 schematically illustrates use of video frame pairs with modifiedexposure times. In an example embodiment, we will consider only a video.The exposure times of the frames are modified from the example of FIG. 1to provide a better response to a low-light scene. Traditionally, theexposure times of all the frames are equal (with t₀) as illustrated atFIG. 1. In the example of FIG. 3, the images may be grouped in pairs210, 220, wherein the exposure time of a pair is 2t₀, just as are twoframes 110 in FIG. 1. FIG. 3 differs from FIG. 1, however, because for apair in FIG. 3, there is an under-exposed frame 310 (with exposure timekt₀, k<1) and an “over-exposed” image 320 (with exposure time of(2−k)t₀). The “over-exposed” frames 320 are used for a better detectionof the appropriate luminance level and of the color gamut, and thereforeto enhance the under-exposed frames 310.

Choosing k: The enhancement method has a limitation. There is a maximumdifference between the exposures of the two images (well exposed 320 andunder-exposed frame 310), when the method works optimally. If theexposure difference is larger than this limit, the under-exposed image310 will have more noise than is typically tolerated in a useful signal.The k is preferably chosen as small as possible (to expose as well aspossible the “swell-exposed image” 320), but its value is preferablykept in the mentioned method limits. Also, the exposure time of thewell-exposed image 320, (2−k)t₀, is preferably not larger than the valuechosen by the auto-exposure (which may be used. as a global reference).

Video Frame Triplets with A Single Well Exposed Image

FIG. 4 schematically illustrates a further embodiment which uses videoframe triplets including one (or more) well-exposed image(s) 420 eachwith two or more under-exposed frames 410, 412. This embodiment providesa natural extension of the previous one described above with referenceto FIG. 3, because the enhancement method illustrated at FIG. 3 does notrequire an order of the two images 310, 320. Therefore, the luminanceand/or color information from the well exposed image 420 may be used toenhance the previous frame 410, as well as in the next frame 412. Insuch a scheme, as illustrated at FIG. 4, the maximum exposure may reachhigher values, and the overall frame rate may be better from the pointof view of the edges. In principle, each well-exposed image 420 may beused to enhance still further combinations of under-exposed images,e.g., two before and/or two after, or one before and two after, or oneafter and two before, or three before and/or after, etc.

Dual Frame Acquisition Pipeline

FIGS. 5 a-5 d schematically illustrate dual frame acquisition pipelineembodiments. FIGS. 5 a-5 d schematically illustrate video frameenhancement involving use of luminance and/or color data from awell-exposed image, and applying the data to one or more relatively lessexposed, sharper image(s). FIGS. 5 a-5 d illustrate four alternativeexamples that are each in accordance with a fourth embodiment whichinvolves at least two image acquisition sub-systems, where the timeparameter is understood to go from left to right in FIGS. 5 a-5 d fromearlier to later. In general, a well exposed image is captured with afirst image acquisition sub-system that is optimized for longerexposure, while a relatively less exposed and sharper image is capturedwith a second sub-system that is particularly optimized for sharpness.

FIG. 5 a illustrates short-exposure time (SET) frames 502 which aresharp, but underexposed. These frames 502 are aligned with the start ofthe full exposure time (FET) frames 504 with normal exposure, fullcolor, but blurred. These frames 502, 504 are combined to generateenhanced video frames 508. FIG. 5 b shows the case where the SET frames502 are acquired towards the end of the FET frames 504. This illustratesthat SET frames 502 can be acquired any time during the FET frame 504 inthis embodiment.

FIGS. 5 a-5 b illustrates an embodiment wherein the elements 502indicate video frames 502 that are acquired with shorter exposure timesthan element 504. This can be understood from the narrower extent of theframes 502 in the time dimension than the frames 504. The frames 504 areexposed for two to ten times as long (or longer, or just under 2× insome embodiments) compared with the frames 502, while in FIGS. 5 a-5 dthe frames 504 are about 5× wider than the frames 502 indicating anexposure time of about 5× longer than for frames 504. The imagecombining unit (ICU) 506 combines luminance and/or color informationfrom the frames 504 to enhance the frames 502. The combinations areimages 508.

In FIG. 5 a, each image 502 is acquired beginning about the same time asa corresponding image 504, even though the exposure of image 502 isended longer before the exposure of image 504 is ended. In FIG. 5 b,each image 502 is acquired in the last moment of acquisition of acorresponding frame 504, i.e., the exposures of the two IAS's are endedat about the same time even though the exposure of frame 504 was begunfar sooner than that of image 502. Another embodiment would have theexposure of image 504 begin before the beginning of the exposure ofimage 502, and the exposure of image 502 is ended before the exposure ofimage 504 is ended, i.e., the frame 502 is acquired in the somewhere inthe middle of the exposure of frame 504.

FIG. 5 c illustrates a case of multiple SET frames 512 acquired withinan exposure duration of a single FET frame 514. Each SET frame 512 canact as a “sharpening reference” for the FET frame 514 enabling multipleenhanced video frames to be resolved. This is advantageous for examplein very low light, where it might take as long as 0.5 seconds for asensor to achieve a full exposure. Using multiple SETs 512 within that0.5 seconds permits a reasonable frame rate of 10-15 fps to be achievedwith enhanced output frames in terms of sharpness, color and/orluminance.

FIG. 5 c schematically illustrates a further embodiment where multiple,e.g., three, short exposure time (SET) frames 512 are acquired while asingle longer exposure time frame (FET) 514 is acquired. In anotherexample, five short exposure time frames 512 are acquired while a singlelonger exposure time frame 524 is acquired. In another example, sevenshort exposure time frames 512 are acquired while a single longerexposure time frame 534 is acquired. Alternatively, the shorter exposuretime frames could be varied as well. In the first example of three SETsper FET, the ICU 516 combines the color and/or luminance informationfrom frame 514 with each of the three frames 512 that were acquiredduring the exposure duration of the frame 514. The results are the threeoutput images 518.

In FIG. 5 c, the second (and subsequent) SET frames 512 could becombined with the first output video frame 518 rather than with the mainFET frame 514 in the same way as an embodiment of the single acquisitionchannel aspect. Thus, in the example of FIG. 5 d, the SETs and FETs maybe similar to those described with reference to FIG. 5 c. In thisexample, the color and/or luminance information initially extracted fromframe 524 is applied to 522 at ICU 526 to get a first processed frame528. In this example, color and/or luminance information is extractedfrom that first processed frame 528 and combined at ICU 526 with one ormore subsequent shorter exposure frames 522 to get one or moresubsequent processed frames 528. This example is particularly applicablealso to the single IAS embodiment except without having temporaloverlap.

In this fourth embodiment, a video camera incorporates two distinctimage acquisition subsystems (IAS). In certain embodiments, each of thetwo IAS's includes at least an image sensor & (digital) post-processingcomponents.

The first IAS may have an image sensor configured to acquire images at ahigher frame rate and with optimal image sharpness. The frame rate forthis first sensor may optionally be fixed and it may optionallyincorporate an image buffer to temporarily store a plurality of thesesharp images.

The second image acquisition subsystem may be configured to capture anoptimally exposed image. As such, it should have a variable frame rateto allow for correct image exposure, even in low lighting conditions.

A timing or clocking unit may be used to maintain temporalsynchronization between the two IAS's and to ensure that images in thefast IAS image buffer can be correctly matched to images obtained fromthe optimally exposed IAS. This timing function may be implementedeither as a hardware unit, or as part of the firmware of a main CPU orDSP.

An additional image combining unit (ICU) selects one (or more) imagesfrom the fast IAS buffer and a corresponding image from the optimallyexposed IAS buffer. The ICU may perform various operations such as thosedescribed at U.S. Ser. Nos. 12/330,719 and/or 11/856,721, which areincorporated by reference. The ICU may also be used with any of thefirst, second or third embodiments described above with references toFIGS. 2-4. The ICU generates a sequence of output images which combinethe one or more sharper, underexposed images from the fast IAS bufferwith the single optimally exposed image obtained from the optimallyexposed IAS.

The system of the fourth embodiment may acquire images of both the fastIAS and the optimally exposed IAS with a same lens as optical input.That input is then split first and second image sensors. Alternatively,images may be acquired separate lens/sensor combinations. Such multiplelens subsystem may include 2, 3, 4 or more lenses. For example, U.S.Pat. No. 7,453,510, which is incorporated by reference, describes amulti-lens subsystem having particular embodiments with four lenses.

Parallax correction may also be provided, as has been provided in thepast in “twin reflex” cameras. When the imaging device incorporates asensor for measuring distance-to-subject, the resulting measure to theprinciple subject of the image may be employed to further enhance theparallax correction, and/or to determine if such correction is needed.When the imaging device incorporates a face detector and/or a facetracking unit, information regarding the size(s) of face(s) detected inthe image may be used to further enhance the parallax correction, and/orto determine if such correction is needed. In general, when a subject isbeyond a certain distance or “critical distance” (infinite focallength), e.g., three or four meters in common cameras, then parallaxcorrection loses its advantage.

Techniques described in US published application 2007/0296833 and/orU.S. Ser. No. 12/116,140, which are incorporated by reference, may becombined with features described herein, particularly to improve theacquisition, or pre-processing of the input images to the ICU, and/or toselectively enhance the output images from this unit.

Output images may be subsequently compressed to form an MPEG videosequence. US published application 2007/0025714 is incorporated byreference. In addition, the techniques described herein may be appliedto a still image camera, whereas the sequence of images may be preview,post-view and/or in-whole or in-part contemporaneously acquired imagesthat are generally captured to enhance capture conditions and/orpost-processing of a main still image.

In a variant of the dual IAS embodiment, both IAS subsystems may share acommon image sensor which employs a modified architecture. Thisembodiment does not have separate optical acquisition subsystems andassociated parallax correction which would be involved in capturingclose-up or portrait images.

In this variant embodiment, an image sensor may be partitioned such thatevery second row of sensor pixels is tied to a separate clock circuit.Thus, the acquisition time of the odd-numbered rows of the image sensorcan be controlled independently of the even-numbered rows. Similarly thedata outputs (pixel values) of these even and odd rows can be loadedonto independent data buses. Thus, by setting different acquisitiontimes for the odd and even rows of sensor pixels, closely overlappingunderexposed and normally exposed images may be advantageously acquired.Due to the close proximity of the odd and even pixel rows, there is asmall, regular half-pixel offset in either horizontal or verticalorientation which can be compensated for, and as both underexposed andnormally exposed images are acquired via that same optics subsystem,there is no parallax correction involved. As in other embodiments, thetwo independently acquired images may be combined using a single passadaptive filter.

Bayer Pattern Partitioning of the Sensor

In another embodiment pairs of rows are linked for each of the differentexposure times. Thus, an entire RGB Bayer set corresponding to a singleRGB pixel will have the same exposure time i.e., rows n+1, n+2 have ashort exposure, while rows n+3, n+4 have a normal (less sharp orrelatively more blurred) exposure.

Considering the exposure time of the underexposed rows is T_(U), whilefor the normally exposed rows is T_(N), an example acquisition procedureis as follows:

Start exposure for all rows of the image sensor (i.e., for both theunderexposed rows and the normally exposed rows);

After (T_(N)-T_(U)) seconds, reset (or discharge) the odd rows;

After T_(N), all the rows are read (i.e., both the underexposed andnormally exposed rows). Two images are formed with half resolution; and

The underexposed image is interpolated to full resolution.

An example choice is to have T_(N)=k T_(U), where k is an integerscalar. This means that the normal exposure time is a multiple of theshort exposure time. Such constraint may be met, e.g., if the exposuretime is reduced by an amount of Ev (or Fstop) values. For instance, anunder-exposure with one (1) Fstop implies T_(N)=2 T_(U). This constrainthas at least the following benefits:

Using the same sampling frequency, all the locations (from the imagesensor) can be read synchronously;

When all the operations are pixel-wise (or use only pixels from twoconsecutive rows), there is no need for an extra image buffer. Theresulting image is built in real-time, while reading. The interpolationoperation is performed locally.

An advantage of this split-sensor acquisition embodiment is that the twoimages are spatially aligned (insofar as is possible given theconstraint that one image is blurred) and hence pixel-wise (for eachlocation independently) operations are possible without a need toacquire and align the entire images.

A further advantage is that the acquisition of the two images canhandled by two independent data busses, enabling the two images to beobtained with a close temporal overlap.

Image Mixing

This offers an alternative approach to the combination of the two imagesusing a single pass adaptive filter. In one example, a process mayinvolve the following two steps:

The first step is about combining the underexposed image F and theblurred image G, by some point-wise amplification algorithm to producean image, called F_(amp), and which has a luminance and color levels atleast very close to the ones present in the blurred image G. Theresulting image F_(amp) has reasonable, but not perfect, luminance andcolor levels. Because the amplification is performed on each pixelindependently, the amplified image will have the same resolution as theunder-exposed image, which is the desired resolution.

As a second step, the final image, F_(out) may be computed as a linearcombination (implemented independently on each pixel) between theblurred image, G, and the amplified image F₁. An example solution toperform this operation is:

Use the YUV plane for performing the calculus;

A luminance of the output image may be expressed as:

Y(F _(out))=0.9*Y(F _(amp))+0.1*Y(G);

A color difference plane of the output image may be expressed as:

U(F _(out))0.3*U(F _(amp))+0.7*U(G),   (i)

V(F _(out))=0.3*V(F _(amp))+0.7*V(G).   (ii)

The system of the fourth embodiment may be applied to other fields ofimage processing. For example, improved Dynamic Range Compression (DRC)may be achieved using a pair of symmetrical, synchronized sensors. Inthis embodiment, one of the pair of symmetrical, synchronized sensorsmay be used to expose correctly, while the other is used to captureover-exposed images, or under-exposed images. The dark areas, or lightareas, can be improved drastically, e.g., in terms of increasedsharpness, color balance, and/or white balance, and/or reducedblurriness.

In another example, hand motion compensation and low lightingvideo/still image enhancement can be improved. In this example, onenormally exposed image and another under-exposed image (e.g.,half-exposed, one-third exposed, one-quarter exposed, one-fifth exposed,or less). Adaptive filtering may be used to combine the images.

In a further embodiment, a third dimension may be added to an image.This feature can be used in an enhanced face recognition technique, orto render, process, store, transmit or display an improved 3Drepresentation.

In another embodiment, improved face tracking is performed. In thiscase, two face detections are performed on two different image streams.One detection may be over-exposed (or under-exposed), and the other maybe normally exposed. In this case, e.g., back-lit objects and otherdifficult lighting conditions can be advantageously handled moreefficiently and effectively and with improved results.

In another embodiment, red eye detection and correction is improvedusing a still image version of the dual frame pipeline embodiment. Therecan appear color exact shifts between pictures obtained by two suchsensors. That can provide an advantageous verification filter, e.g., toconfirm that detected red pixels are indeed red eye artifacts.

In a further embodiment, foreground/background separation techniques canbe enhanced using a dual frame pipeline. For example, one sensor maycapture a focused image, while the other is used to capture an at leastslightly de-focused image. Advantageous separation between backgroundand foreground can be thereby achieved allowing for the creation of highquality portraits with inexpensive and/or relatively simple optics.

In another example, one sensor may be used to capture IR images orimages that include an IR component. Such sensor can be provided byremoving an IR filter of certain sensors and/or adding a visible lightfilter. Such IR sensor would be advantageous in performing imageprocessing and image capture in lowlight conditions, and in a stillimage embodiment for performing red eye detection and correction.

Other examples include noise reduction and/or processes involvingcapturing non-scene shot images to be further used as additional camerafeatures. For example, an eye iris analysis tool may be embedded in adigital cameras that has an eyepiece viewfinder. The image of the irislooking through the eyepiece may be captured by the camera CCD, or anadditional CCD, after being diverted by one or more optics. The image ofthe iris may be analyzed and used for biometric user identification(camera lock, digital picture watermarking), inferring lightingconditions, detecting user fatigue, and/or detecting certain symptoms ofa medical condition of a user.

A low-resolution camera looking back at a user's face may be embedded ina digital camera. The image of the user's face may be captured by thecamera CCD, or an additional CCD, after being acquired and processed byone or more optics. This can be used for face identification for camerausage protection, IP protection for digital pictures, and/or analysis ofuser emotions based on the face and/or as feed-back of the user emotionsinto the captured image itself.

In another embodiment that is particularly advantageous for lowlightconditions, a reduced frame rate may sometimes be used in order toincrease the exposure duration to gather more light. If multiple sensorsare used, e.g., two (although three or more may be used), then a fasterframe rate will result in sharper images. For example, even frames maybe acquired with one sensor, and odd frames with another sensor (or forthree sensors, every third frame is acquired with each of the threesensors, or for four sensors, etc).

The sensors will generally have the same exposure (e.g., for twosensors, the time T may be about twice the frame rate), but one sensorwill start acquiring image data at t=0, and the second sensor will startat t=T/2.

Alternative to the previous embodiment that is particularly advantageousfor lowlight conditions, instead of or in addition to increasing (ordecreasing) exposure time, a larger aperture can be set. While depth offield will be smaller such that a subject with background would bedefocused, the frame rate can be advantageously higher than the exampleof increasing the exposure time. With dual sensors and optical elements,both lenses can be set to large aperture, where one is focused on thebackground and the other is on the subject. The two resulting picturescan be combined, in one high-frequency picture, where both the subjectand background are in focus (the two images are complementary, where onehas high frequencies the other has low frequencies). So in lowlight,exposure time can be kept short and ISO small, with fully open aperture,wherein two short DoF images are combined into one with good focus bothon subject and background.

In a de-noising algorithm, two images can be acquired with oneoverexposed and the other normally exposed. The normally exposed imagemay be de-noised using information from the overexposed image. Anadaptive algorithm may be used as a function of illumination of thepixels, because lower illuminated pixels exhibit greater noise.

In a further embodiment, a two lens system can be used in anotherembodiment as follows. One lens may capture certain scenery broadly,e.g., a tourist either standing relatively close to a camera with theEgyptian pyramids far away from the camera and tourist, or the touriststanding further from the camera and closer to the pyramids and lookingvery small. The other lens is used to zoom and focus on the tourist orother main subject from the scene.

A single file or multiple files may then store the two images. The twoimages can be acquired at the same time with a system in accordance withthe dual image pipeline embodiment, or proximate in time in the singleoptical system embodiments. An advantage is that, while having apanoramic image, there will still be excellent detail in the main partor subject of the scene (e.g., the tourist or more particularly the faceof the tourist). In one embodiment, the wide-angle scene may use a facetracker to determine the location of a face or faces in the scene, andthe zoom/aperture of the second imaging system may be adjusted toinclude people detected in the captured image. In an alternativeembodiment, both wide-angle and narrow angle images of the scene may becaptured and subsequently combined into one or more composite images. Inanother embodiment, selective high-quality compression of a face regionmay be enabled in a portrait (e.g., using a zoom lens), withlower-quality compression applied to the background image (e.g., using awide-angle lens).

Wavefront coding may also be provided. Variable focus is used fordifferent parts of a lens. Various parts of the lens capture informationrelating to different focal points. The image is decoded according toknown defocus variations and a resulting image has an extended depth offield. CDM Optics have studied this technology, andhttp://www.cdm-optics.com is incorporated by reference.

Phase retrieval and/or phase diversity may also be provided. Two imagesare captured simultaneously with a system in accordance with the dualpipeline embodiment. One image is in focus, and another is defocused bya known distance. The two images are recombined and the known defocusdistance which distorts the image is used to reconstruct the image witha greater depth of field. A beam splitter could also be used to capturethe defocused image to apply phase diversity.

While an exemplary drawings and specific embodiments of the presentinvention have been described and illustrated, it is to be understoodthat that the scope of the present invention is not to be limited to theparticular embodiments discussed. Thus, the embodiments shall beregarded as illustrative rather than restrictive, and it should beunderstood that variations may be made in those embodiments by workersskilled in the arts without departing from the scope of the presentinvention as set forth in the claims that follow and their structuraland functional equivalents.

In addition, in methods that may be performed according to preferred andalternative embodiments and claims herein, the operations have beendescribed in selected typographical sequences. However, the sequenceshave been selected and so ordered for typographical convenience and arenot intended to imply any particular order for performing theoperations, unless a particular ordering is expressly indicated as beingrequired or is understood by those skilled in the art as beingnecessary.

Many references have been cited above herein, and in addition to thatwhich is described as background, the invention summary, briefdescription of the drawings, the drawings and the abstract, thesereferences are hereby incorporated by reference into the detaileddescription of the preferred embodiments, as disclosing alternativeembodiments of elements or features of the preferred embodiments nototherwise set forth in detail above. A single one or a combination oftwo or more of these references may be consulted to obtain a variationof the preferred embodiments described in the detailed descriptionabove. In addition, the following are incorporated by reference,particularly for this purpose: US2005/0041121, US2008/0043121,2006/0204034, WO/2007/142621, U.S. Ser. No. 10/764,339, U.S. Pat. No.7,369,712, US2005/0068452, US2006/0120599, 2006/0098237, US2006/0039690,U.S. Ser. No. 11/573,713, U.S. Ser. No. 12/042,335, US2007/0147820,US2007/0189748, US2009/0003652, and U.S. Pat. Nos. 7,336,821, 7,315,630,7,316,631, 7,403,643, and 7,460,695, and WO/2008/017343, US2007/0269108,US2007/0296833, US2008/0292193, US2008/0175481, U.S. Ser. No.12/042,104, U.S. Ser. No. 12/330,719, U.S. Ser. No. 11/856,721, U.S.Ser. No. 12/026,484, U.S. Ser. No. 11/861,854, U.S. Ser. No. 12/354,707,and U.S. Ser. No. 12/336,416. In addition, US published applicationsnos. 2003/0169818, 20030193699, 20050041123, 20060170786, and20070025714 are incorporated by reference, particularly as disclosingalternative embodiments relating to still image cameras and/or thefourth embodiment “Dual image Acquisition Pipeline”.

1. A method of combining image data from multiple frames to enhance oneor more parameters of digital image quality, comprising using aprocessor and at least one digital image acquisition system including alens and an image sensor in: acquiring a first image at a first exposureduration; acquiring a second image at a second exposure duration shorterthan the first exposure duration and at a time just before, just afteror overlapping in time with acquiring the first image, such that saidfirst and second images comprise approximately a same first scene, andwhereby the second image is relatively sharp and under-exposed and thefirst image is relatively well-exposed and less sharp than the secondimage; extracting brightness or color information, or both, from thefirst image; applying to the second image the brightness or colorinformation, or both, extracted from the first image to generate anenhanced version of the second image enhanced in terms of brightness orcolor quality, or both; and displaying, storing, transmitting, orstreaming the enhanced version of the second image.
 2. The method ofclaim 1, further comprising applying to one or more further images thebrightness or color information, or both, extracted from the first imageto generate enhanced versions of the one or more further images enhancedin terms of brightness or color quality, or both.
 3. The method of claim2, wherein the one or more further images are acquired at or near thesecond exposure duration and at a time or times just before or justafter, or both, the acquiring of the second image, such that said one ormore further images comprise approximately said same scene as said firstand second images.
 4. The method of claim 1, further comprising:acquiring a third image at or near said first exposure duration when apredetermined number of multiple frames has been recorded since theacquiring of the first image; acquiring a fourth image at or near saidsecond exposure duration and at a time just before, just after oroverlapping in time with the third image, such that said third andfourth images comprise approximately a same second scene different fromor same as the first scene; extracting brightness or color, or both,from the third image; applying to the fourth image the brightness orcolor information, or both, extracted from the third image to generatean enhanced version of the fourth image enhanced in terms of brightnessor color quality, or both; and displaying storing, transmitting, orstreaming the enhanced version of the fourth image.
 5. The method ofclaim 1, further comprising: acquiring a third image at or near saidfirst exposure duration when a predetermined amount of camera movementhas been detected since the acquiring of the first image; acquiring afourth image at or near said second exposure duration and at a time justbefore, just after or overlapping in time with the third image, suchthat said third and fourth images comprise approximately a same secondscene different from the first scene due at least to said cameramovement; extracting brightness or color, or both, from the third image;applying to the fourth image the brightness or color information, orboth, extracted from the third image to generate an enhanced version ofthe fourth image enhanced in terms of brightness or color quality, orboth; and displaying, storing, transmitting, or streaming the enhancedversion of the fourth image.
 6. The method of claim 1, furthercomprising: acquiring a third image at or near said first exposureduration including combining some of the data from the first image withsome or all of the data from the second image; acquiring a fourth imageat or near said second exposure duration and at a time just before, justafter or overlapping in time with the third image, such that said thirdand fourth images comprise approximately said same first scene;extracting brightness or color information, or both, from the thirdimage, applying to the fourth image the brightness or color information,or both, extracted from the third image to generate an enhanced versionof the fourth image enhanced in terms of brightness or color quality, orboth; and displaying, storing, transmitting, or streaming the enhancedversion of the fourth image.
 7. The method of claim 6, furthercomprising repeatedly iterating the method as the scene evolves withtime or camera movement or both.
 8. The method of claim 6, furthercomprising: iteratively alternating acquisition of well-exposed andsharp, under-exposed images; extracting brightness or color information,or both, from tile well-exposed images; and applying to the sharp,under-exposed images the brightness or color information, or both,extracted from the well-exposed images to generate enhanced versions ofthe sharp, under-exposed images enhanced in terms of brightness or colorquality, or both; and displaying, storing, transmitting, or streamingthe enhanced versions of the sharp, under-exposed images.
 9. The methodof claim 1, further comprising iteratively performing the following:acquiring two sharp, under-exposed frames and a well-exposed frame;extracting brightness or color information, or both, from thewell-exposed frame; applying to each pair of sharp, under exposed imagesrespectively captured immediately before and immediately after theacquiring of each well-exposed frame the brightness or colorinformation, or both, extracted from the well-exposed frame to generateenhanced versions of each of the pair of sharp, under-exposed imagesenhanced in terms of brightness or color quality, or both; anddisplaying, storing, transmitting, or streaming the enhanced versions ofthe pair of sharp, under-exposed images.
 10. The method of claim 1,further comprising utilizing separate image acquisition subsystems(IAS's) for acquiring the first and second images.
 11. The method ofclaim 10, wherein the separate IAS's comprise first and second IAS's,wherein the first IAS is configured to acquire images at a faster framerate than the second IAS, such that the first IAS is speciallyconfigured to capture relatively sharp, under-exposed images and thesecond IAS is specially configured to capture well-exposed and lesssharp images.
 12. The method of claim 11, wherein the first IAS has afixed frame rate.
 13. The method of claim 11, wherein the second IAS hasa variable frame rate configured for capturing optimally-exposed imagesunder different lighting conditions.
 14. The method of claim 10, furthercomprising acquiring both the first and second images with a same lensas optical input, and splitting the optical input between first andsecond image sensors.
 15. The method of claim 10, further comprisingacquiring the first and second images, respectively, with a firstlens/sensor combination and a second lens/sensor combination.
 16. Themethod of claim 15, further comprising applying parallax correction. 17.A digital image acquisition system, comprising a lens, an image sensorfor capturing a stream of multiple digital images, a processor and amemory having processor-readable code embedded therein for programmingthe processor to perform a method of combining image data from multipleframes to enhance one or more parameters of digital image quality,wherein the method comprises: acquiring a first image at a firstexposure duration; acquiring a second image at a second exposureduration shorter than the first exposure duration and at a time justbefore, just after or overlapping in time with acquiring the firstimage, such that said first and second images comprise approximately asame first scene, and whereby the second image is relatively sharp andunder-exposed and the first image is well-exposed and less sharp thanthe second image; extracting brightness or color information, or both,from the first image; applying to the second image the brightness orcolor information, or both, extracted from the first image to generatean enhanced version of the second image enhanced in terms of brightnessor color quality, or both.
 18. The system of claim 17, wherein themethod further comprises applying to one or more further images thebrightness or color information, or both, extracted from the first imageto generate enhanced versions of the one or more further images enhancedin terms of brightness or color quality, or both.
 19. The system ofclaim 18, wherein the one or more further images are acquired at or nearthe second exposure duration and at a time or times just before or justafter, or both, the acquiring of the second image, such that said one ormore further images comprise approximately said same scene as said firstand second images.
 20. The system of claim 17, wherein the methodfurther comprises: acquiring a third image at or near said firstexposure duration when a predetermined number of multiple frames hasbeen recorded since the acquiring of the first image; acquiring a fourthimage at or near said second exposure duration and at a time justbefore, just after or overlapping in time with the third image, suchthat said third and fourth images comprise approximately a same secondscene different from or same as the first scene; extracting brightnessor color, or both, from the third image; applying to the fourth imagethe brightness or color information, or both, extracted from the thirdimage to generate an enhanced version of the fourth image enhanced interms of brightness or color quality, or both; and displaying, storing,transmitting, or streaming the enhanced version of the fourth image. 21.The system of claim 17, wherein the method further comprises: acquiringa third image at or near said first exposure duration when apredetermined amount of camera movement has been detected since theacquiring of the first image; acquiring a fourth image at or near saidsecond exposure duration and at a time just before, just after oroverlapping in time with the third image, such that said third andfourth images comprise approximately a same second scene different fromthe first scene due at least to said camera movement; extractingbrightness or color, or both, from the third image; applying to thefourth image the brightness or color information, or both, extractedfrom the third image to generate an enhanced version of the fourth imageenhanced in terms of brightness or color quality, or both; anddisplaying, storing, transmitting, or streaming the enhanced version ofthe fourth image.
 22. The system of claim 17, wherein the method furthercomprises: acquiring a third image at or near said first exposureduration including combining some of the data from the first image withsome or all of the data from the second image; acquiring a fourth imageat or near said second exposure duration and at a time just before, justafter or overlapping in time with the third image, such that said thirdand fourth images comprise approximately said same first scene;extracting brightness or color information, or both, from the thirdimage; applying to the fourth image the brightness or color information,or both, extracted from the third image to generate an enhanced versionof the fourth image enhanced in terms of brightness or color quality, orboth; and displaying, storing, transmitting, or streaming the enhancedversion of the fourth image.
 23. The system of claim 22, wherein themethod further comprises repeatedly iterating the method as the sceneevolves with time or camera movement or both.
 24. The system of claim22, wherein the method further comprises: iteratively alternatingacquisition of well-exposed and sharp, under-exposed images; extractingbrightness or color information, or both, from the well-exposed images;and applying to the sharp, under-exposed images the brightness or colorinformation, or both, extracted from the well-exposed images to generateenhanced versions of the sharp, under-exposed images enhanced in termsof brightness or color quality, or both; and displaying, storing,transmitting, or streaming the enhanced versions of the sharp,under-exposed images.
 25. The system of claim 17, wherein the methodfurther comprises iteratively performing the following: acquiring twosharp, under-exposed frames and a well-exposed frame; extractingbrightness or color information, or both, from the well-exposed frame;applying to each pair of sharp, under exposed images respectivelycaptured immediately before and immediately after the acquiring of eachwell-exposed frame the brightness or color information, or both,extracted from the well-exposed frame to generate enhanced versions ofeach of the pair of sharp, under-exposed images enhanced in terms ofbrightness or color quality, or both; and displaying, storing,transmitting, or streaming the enhanced versions of the pair of sharp,under-exposed images.
 26. The system of claim 17, wherein the methodfurther comprises separate image acquisition subsystems (IAS's) foracquiring the first and second images.
 27. The system of claim 26,wherein the separate IAS's comprise first and second IAS's, wherein thefirst IAS is configured to acquire images at a faster frame rate thanthe second IAS, such that the first IAS is specially configured tocapture relatively sharp, under-exposed images and the second IAS isspecially configured to capture well-exposed and less sharp images. 28.The system of claim 27, wherein the first IAS has a fixed frame rate.29. The system of claim 27, wherein the second IAS has a variable framerate configured for capturing optimally-exposed images under differentlighting conditions.
 30. The system of claim 26, wherein the methodfurther comprises acquiring both the first and second images with a samelens as optical input, and splitting the optical input between first andsecond image sensors.
 31. The system of claim 26, wherein the methodfurther comprises acquiring the first and second images, respectively,with a first lens/sensor combination and a second lens/sensorcombination.
 32. The system of claim 31, wherein the method furthercomprises applying parallax correction.
 33. One or moreprocessor-readable media having processor-readable code embedded thereinfor programming one or more processors to perform a method of combiningimage data from multiple frames to enhance one or more parameters ofdigital image quality, comprising: acquiring a first image at a firstexposure duration; acquiring a second image at a second exposureduration shorter than the first exposure duration and at a time justbefore, just after or overlapping in time with acquiring the firstimage, such that said first and second images comprise approximately asame first scene, and whereby the second image is relatively sharp andunder-exposed and the first image is well-exposed and less sharp thanthe second image; extracting brightness or color information, or both,from the first image; applying to the second image the brightness orcolor information, or both, extracted from the first image to generatean enhanced version of the second image enhanced in terms of brightnessor color quality, or both.
 34. The one or more processor-readable mediaof claim 33, wherein the method further comprises applying to one ormore further images the brightness or color information, or both,extracted from the first image to generate enhanced versions of the oneor more further images enhanced in terms of brightness or color quality,or both.
 35. The one or more processor-readable media of claim 34,wherein the one or more further images are acquired at or near thesecond exposure duration and at a time or times just before or justafter, or both, the acquiring of the second image, such that said one ormore further images comprise approximately said same scene as said firstand second images.
 36. The one or more processor-readable media of claim33, wherein the method further comprises: acquiring a third image at ornear said first exposure duration when a predetermined number ofmultiple frames has been recorded since the acquiring of the firstimage; acquiring a fourth image at or near said second exposure durationand at a time just before, just after or overlapping in time with thethird image, such that said third and fourth images compriseapproximately a same second scene different from or same as the firstscene; extracting brightness or color, or both, from the third image;applying to the fourth image the brightness or color information, orboth, extracted from the third image to generate an enhanced version ofthe fourth image enhanced in terms of brightness or color quality, orboth; and displaying, storing, transmitting, or streaming the enhancedversion of the fourth image.
 37. The one or more processor-readablemedia of claim 33, wherein the method further comprises: acquiring athird image at or near said first exposure duration when a predeterminedamount of camera movement has been detected since the acquiring of thefirst image; acquiring a fourth image at or near said second exposureduration and at a time just before, just after or overlapping in timewith the third image, such that said third and fourth images compriseapproximately a same second scene different from the first scene due atleast to said camera movement; extracting brightness or color, or both,from the third image; applying to the fourth image the brightness orcolor information, or both, extracted from the third image to generatean enhanced version of the fourth image enhanced in terms of brightnessor color quality, or both; and displaying, storing, transmitting, orstreaming the enhanced version of the fourth image.
 38. The one or moreprocessor-readable media of claim 33, wherein the method furthercomprises: acquiring a third image at or near said first exposureduration including combining some of the data from the first image withsome or all of the data from the second image; acquiring a fourth imageat or near said second exposure duration and at a time just before, justafter or overlapping in time with the third image, such that said thirdand fourth images comprise approximately said same first scene;extracting brightness or color information, or both, from the thirdimage; applying to the fourth image the brightness or color information,or both, extracted from the third image to generate an enhanced versionof the fourth image enhanced in terms of brightness or color quality, orboth; and displaying, storing, transmitting, or streaming the enhancedversion of the fourth image.
 39. The one or more processor-readablemedia of claim 38, wherein the method further comprises repeatedlyiterating the method as the scene evolves with time or camera movementor both.
 40. The one or more processor-readable media of claim 38,wherein the method further comprises: iteratively alternatingacquisition of well-exposed and sharp, under-exposed images; extractingbrightness or color information, or both, from the well-exposed images;and applying to the sharp, under-exposed images the brightness or colorinformation, or both, extracted from the well-exposed images to generateenhanced versions of the sharp, under-exposed images enhanced in termsof brightness or color quality, or both; and displaying, storing,transmitting, or streaming the enhanced versions of the sharp,under-exposed images.
 41. The one or more processor-readable media ofclaim 33, wherein the method further comprises iteratively performingthe following: acquiring two sharp, under-exposed frames and awell-exposed frame; extracting brightness or color information, or both,from the well-exposed frame; applying to each pair of sharp, underexposed images respectively captured immediately before and immediatelyafter the acquiring of each well-exposed frame the brightness or colorinformation, or both, extracted from the well-exposed frame to generateenhanced versions of each of the pair of sharp, under-exposed imagesenhanced in terms of brightness or color quality, or both; anddisplaying, storing, transmitting, or streaming the enhanced versions ofthe pair of sharp, under-exposed images.
 42. The one or moreprocessor-readable media of claim 33, wherein the method furthercomprises utilizing separate image acquisition subsystems (IAS's) foracquiring the first and second images.
 43. The one or moreprocessor-readable media of claim 42, wherein the separate IAS'scomprise first and second IAS's, wherein the first IAS is configured toacquire images at a faster frame rate than the second IAS, such that thefirst IAS is specially configured to capture relatively sharp,under-exposed images and the second IAS is specially configured tocapture well-exposed and less sharp images.
 44. The one or moreprocessor-readable media of claim 43, wherein the first IAS has a fixedframe rate.
 45. The one or more processor-readable media of claim 43,wherein the second IAS has a variable frame rate configured forcapturing optimally-exposed images under different lighting conditions.46. The one or more processor-readable media of claim 42, wherein themethod further comprises acquiring both the first and second images witha same lens as optical input, and splitting the optical input betweenfirst and second image sensors.
 47. The one or more processor-readablemedia of claim 42, wherein the method further comprises acquiring thefirst and second images, respectively, with a first lens/sensorcombination and a second lens/sensor combination.
 48. The one or moreprocessor-readable media of claim 47, wherein the method furthercomprises applying parallax correction.
 49. The method of claim 1,wherein the first and second images comprise video images of a videostream.
 50. The system of claim 17, wherein the first and second imagescomprise video images of a video stream.
 51. The one or moreprocessor-readable media of claim 33, wherein the first and secondimages comprise video images of a video stream.